1.Field of the Invention
The present invention relates to an injector head for medical use, and more particularly relates to an improvement of the structure of the injector head for medical use.
2.Description of the Background Art
Various apparatuses for testing the function of the human body have been developed recently. One example is a circulatory organ X-ray diagnostic apparatus for diagnosing the function of the circulatory organ of the human body. With reference to FIG. 15, a general description of the circulatory organ x-ray diagnostic apparatus will be given.
A circulatory organ X-ray diagnostic apparatus 1000 is provided with a rail 103 attached to a ceiling 101. An X-ray apparatus 102 which is movable freely in X and Y directions is attached to rail 103. A cartheter table 104 for laying a patient 106 at a prescribed position is arranged at a prescribed position.
A side of cartheter table 104 has a guide rail 108. Guide rail 108 has an equipment attached for performing the procedure necessary for the X-ray diagnosis for patient 106. In FIG. 15, for example, a support unit 200 is mounted on guide rail 108, and an injector head for medical use 100 for injecting the contrast medium into patient 106 is attached to support unit 200 via a stanchion 114. By moving support unit 200 along guide rail 108, medical injector head 100 can be positioned at patient 106, and interference with any other apparatus can be avoided.
With reference to FIGS. 16 and 17, a structure of medical injector head 100 is generally described. Note that FIG. 16 is a perspective view illustrating an internal structure of medical injector head 100 and FIG. 17 shows an arrangement of internal units viewing from the rear side of medical injector head 100.
A syringe 120 having a piston 121 provided therein is attached to medical injector head 100. A plunger 122 provided to injector head 100 is coupled to piston 121. The contrast medium contained in syringe 120 can be injected to a patient by moving plunger 122 forward. On the other hand, backward movement of plunger 122 causes the contrast medium to be sucked in syringe 120.
A ball screw (not shown) is attached to a rear end of plunger 122. By rotating the ball screw using a plunger motor 130, forward and backward movements of plunger 122 can be controlled.
Plunger 122 is also provided with a position plate 123. Position plate 123 moves with plunger 122 following the movement of plunger 122. When position plate 123 meets a mechanical stopper 129 described below, the forward movement of plunger 122 is mechanically impeded. Accordingly, even if an electrical control device for medical injector head 100 fails, the safety of mechanical injector head 100 is assured by mechanically restraining plunger 122 from moving.
Four corners of position plate 123 are guided by guide rods 124 provided in a body frame 110.
Mechanical stopper 129 also serves as a nut of the ball screw. Mechanical stopper 129 can be positioned at a prescribed position by rotating a screw axis 128 of the ball screw. As shown in FIG. 17, mechanical stopper 129 is also guided by diagonally placed guide rods 124.
Screw axes 128a and 128b are placed at diagonal positions in mechanical stopper 129. Pulleys 127a and 127b are provided at the ends of screw axes 128a and 128b. A belt 126 is wound around pulleys 127a and 127b. A turning force of a mechanical stop motor 125 is transmitted to screw axes 128a and 128b via pulleys 127c and 127d. Positioning of mechanical stopper 129 can be controlled by utilizing a position meter (not shown) provided to mechanical stop motor 125.
A safety mechanism adopted by the injector head can be summarized as follows. Even if an electrical device for controlling plunger 122 fails and a signal which causes plunger 122 to move forward without stopping is transferred, position plate 123 comes into contact with mechanical stopper 129 placed at a prescribed position thereby mechanically stopping plunger 122.
The structure of the conventional injector head for medical use described above has a problem below.
Referring again to FIGS. 16 and 17, a hole 129h for passing plunger 122 therethrough is provided at the central portion of mechanical stopper 129 provided to medical injector head 100. In order to drive mechanical stopper 129 in a stable state such that it does not move out of its proper position, nut screws are placed diagonally at two positions.
Specifically, as shown in FIG. 18, suppose that a force applied from position plate 123 to mechanical stopper 129 is f.sub.1, a reaction force f.sub.2 is generated at the positions of the two nut screws supporting mechanical stopper 129. As a result, mechanical stopper 129 is brought into a stable state by force f.sub.1 and reaction force f.sub.2 at two positions. Mechanical stopper 129 is thus driven to function in the stable state without moving out of its proper position in the direction shown by A in the figure.
Since nut screws are placed at two positions of mechanical stopper 129, medical injector head 100 becomes large. Further, synchronized operation of two nut screws requires pulleys 127a, 127b, 127c, 127d and belt 126, resulting in a complex structure of the device.